Chandra X-Ray and Hubble Space Telescope Imaging of Optically Selected Kiloparsec-Scale Binary Active Galactic Nuclei. Ii. Host Galaxy Morphology and Agn Activity*

We present Chandra and optical observations of a candidate dual AGN discovered serendipitously while searching for recoiling black holes via a cross-correlation between the serendipitous XMM source catalog (2XMMi) and SDSS-DR7 galaxies with a separation no larger than ten times the sum of their Petrosian radii. The system has a stellar mass ratio M 1 /M 2 ≈ 0.7. One of the galaxies (Source 1) shows clear evidence for AGN activity in the form of hard X-ray emission and optical emission-line diagnostics typical of AGN ionisation. The nucleus of the other galaxy (Source 2) has a soft X-ray spectrum, bluer colours, and optical emission line ratios dominated by stellar photoionisation with a "composite" signature, which might indicate the presence of a weak AGN. When plotted on a diagram with X-ray luminosity vs [OIII] luminosity both nuclei fall within the locus defined by local Seyfert galaxies. From the optical spectrum we estimate the electron densities finding n 1 < 27 e − cm −3 and n 2 ≈ 200 e − cm −3 . From a 2D decomposition of the surface brightness distribution we infer that both galaxies host rotationally supported bulges (Sersic index < 1). While the active nature of Source 1 can be established with confidence, whether the nucleus of Source 2 is active remains a matter of debate. Evidence that a faint AGN might reside in its nucleus is, however, tantalising.

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“…As in Liu et al 2013 andShangguan et al 2016 we find hard X-ray emission in the nucleus displaying redder colours.…”

Section: Nuclear Activitysupporting

confidence: 76%

Characterization of a candidate dual AGN

Lena

Panizo-Espinar

Jonker

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…Until recently, only a handful cases of dual active galactic nuclei (AGNs) -galacticscale progenitors of BSBHs -were known (Owen et al 1985;Junkkarinen et al 2001;Komossa et al 2003;Ballo et al 2004;Hudson et al 2006;Max et al 2007;Bianchi et al 2008;Guidetti et al 2008). While great strides have been made in identifying dual AGNs at kpc scales (e.g., Gerke et al 2007;Comerford et al 2009Comerford et al , 2012Comerford et al , 2015Liu et al 2010Liu et al , 2013Liu et al , 2018Green et al 2010;Fabbiano et al 2011;Fu et al 2011Fu et al , 2012Fu et al , 2015aKoss et al 2011Koss et al , 2012Koss et al , 2016Rosario et al 2011;Teng et al 2012;Woo et al 2014;Wrobel et al 2014a;McGurk et al 2015;Müller-Sánchez et al 2015;Shangguan et al 2016;Ellison et al 2017;Satyapal et al 2017), there is no confirmed BSBH at sub-pc scales (for recent reviews, see e.g., Popović 2012;Burke-Spolaor 2013;Bogdanović 2015;Komossa & Zensus 2016).…”

Section: Introductionmentioning

confidence: 99%

Constraining sub-parsec binary supermassive black holes in quasars with multi-epoch spectroscopy – III. Candidates from continued radial velocity tests

Guo

Liu

Shen

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Quasars whose broad emission lines show temporal, bulk radial velocity (RV) shifts have been proposed as candidate sub-parsec (sub-pc), binary supermassive black holes (BSBHs). We identified a sample of 16 BSBH candidates based on two-epoch spectroscopy among 52 quasars with significant RV shifts over a few rest-frame years. The candidates showed consistent velocity shifts independently measured from two broad lines (Hβ and Hα or Mg II) without significant changes in the broad-line profiles. Here in the third paper of the series, we present further third-and fourth-epoch spectroscopy for 12 of the 16 candidates for continued RV tests, spanning ∼5-15 yr in the quasars' rest frames. Cross-correlation analysis of the broad Hβ calibrated against [O III] λ5007 suggests that 5 of the 12 quasars remain valid as BSBH candidates. They show broad Hβ RV curves that are consistent with binary orbital motion without significant changes in the broad line profiles. Their broad Hα (or Mg II) lines display RV shifts that are either consistent with or smaller than those seen in broad Hβ. The RV shifts can be explained by a ∼0.05-0.1 pc BSBH with an orbital period of ∼40-130 yr, assuming a mass ratio of 0.5-2 and a circular orbit. However, the parameters are not well constrained given the few epochs that sample only a small portion of the hypothesized binary orbital cycle. The apparent occurrence rate of sub-pc BSBHs is 13±5% among all SDSS quasars, with no significant difference in the subsets with and without single-epoch broad line velocity offsets. Dedicated long-term spectroscopic monitoring is still needed to further confirm or reject these BSBH candidates.

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“…Therefore, dual-AGN host systems may show a preference for major mergers so that enough fuel is available to power both AGNs. For example, of the threeSDSSdual-AGN systems, two are hosted by major mergers (Shangguan et al 2016). Since the sample from Treister et al (2012) extends to high redshifts and was selected based on morphology, that sample may contain a relatively higher fraction of major mergers that allow for easier visual classification, possibly accounting for the agreement between that sample and the comparison SDSS dual-AGN sample.…”

Section: Triggering Of High-luminosity Agns In Mergersmentioning

confidence: 99%

Spatially Offset Active Galactic Nuclei. II. Triggering in Galaxy Mergers

Barrows

Comerford

Greene

et al. 2017

ApJ

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Galaxy mergers are likely to play a role in triggering active galactic nuclei (AGNs), but the conditions under which this process occurs are poorly understood. In Paper I, we constructed a sample of spatially offset X-ray AGNs that represent galaxy mergers hosting a single AGN. In this paper, we use our offset AGN sample to constrain the parameters that affect AGN observability in galaxy mergers. We also construct dual-AGN samples with similar selection properties for comparison. We find that the offset AGN fraction shows no evidence for a dependence on AGN luminosity, while the dual-AGN fractions show stronger evidence for a positive dependence, suggesting that the merger events forming dual AGNs are more efficient at instigating accretion onto supermassive black holes than those forming offset AGNs. We also find that the offset and dual-AGN fractions both have a negative dependence on nuclear separation and are similar in value at small physical scales. This dependence may become stronger when restricted to high AGN luminosities, although a larger sample is needed for confirmation. These results indicate that the probability of AGN triggering increases at later merger stages. This study is the first to systematically probe down to nuclear separations of <1 kpc (∼0.8 kpc) and is consistent with predictions from simulations that AGN observability peaks in this regime. We also find that the offset AGNs are not preferentially obscured compared to the parent AGN sample, suggesting that our selection may be targeting galaxy mergers with relatively dust-free nuclear regions.

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Chandra X-Ray and Hubble Space Telescope Imaging of Optically Selected Kiloparsec-Scale Binary Active Galactic Nuclei. Ii. Host Galaxy Morphology and Agn Activity*

Cited by 25 publications

References 136 publications

Characterization of a candidate dual AGN

Characterization of a candidate dual AGN

Constraining sub-parsec binary supermassive black holes in quasars with multi-epoch spectroscopy – III. Candidates from continued radial velocity tests

Spatially Offset Active Galactic Nuclei. II. Triggering in Galaxy Mergers

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